The Alphavirus genus in the Togaviridae family contains a number of widely distributed important human and animal pathogens. The New World alphaviruses, which include Venezuelan (VEEV), eastern (EEEV) and western equine encephalitis (WEEV) viruses, represent a serious public health threat in the US and can be applied by bioterrorists. However, to date, neither effective antivirals nor safe and efficient vaccines have been developed for preventing VEEV, EEEV or WEEV infections. The existing experimental vaccines are either of poor efficacy or demonstrate very strong adverse reactions in humans. Our studies of the molecular mechanism of alphavirus pathogenesis provided a unique opportunity to develop a new type of vaccine candidates against encephalitogenic, New World alphaviruses. The generated in the proposed study vaccine candidates will demonstrate i) highly attenuated phenotype, which is based on their inability to interfere with the induction of the innate immune response; ii) the attenuated phenotype will be irreversible due to large number of redundant mutations; iii) the designed mutants will cause an abortive infection in vivo, but they will sustain the ability for replication to high titers in Vero cells. iv) The genomes of the designed viruses will contain additional, extensive modifications, which make these viruses incapable of replicating in mosquito cells and vectors. Thus, they will be excluded from the natural circulation.